ADO: ActiveX Data Objects

Lock Types: Managing Access to a Recordset

There are four record-locking schemes in ADO. Each has its own advantages and disadvantages, as described in the following sections. The record lock type is indicated by either the LockType property of the Recordset object or the LockType parameter of the Open method of the Recordset object. The LockType parameter of the Open method is the fourth parameter in the parameter list.

Either one of these (the parameter or the property) can be set to one of the four valid constants from the LockTypeEnum enumeration shown in Table 5-15.

Table 5-15. The LockTypeEnum Enumeration

Value	Description
adReadOnly	Indicates that the recordset will use a read-only record-locking scheme.
adLockOptimistic	Indicates that the recordset will use an optimistic record-locking scheme.
adLockPessimistic	Indicates that the recordset will use a pessimistic record-locking scheme.
adLockBatchOptimistic	Indicates that the recordset will use a batch optimistic record-locking scheme.

Read-Only Locks

A read-only record-locking scheme is the simplest locking scheme of the four available. Basically, a read-only recordset does not allow adding or editing of records; therefore, the records themselves do not need to be locked for editing at all.

The following example illustrates how to open a recordset with the read-only record-locking scheme:

rst.Open "Authors", _
         "DSN=BiblioDSN", _
         adOpenKeyset, _
         adLockReadOnly

' cannot alter data

rst.Close

You should use read-only ...